ok... I get the same behavior. It's a bug. Probably because the metadata is too big to parse.
However... you don't really need to look at it for now :-)
When you setup a new Trust Relationship, use `Metadata Location: Federation` and select InCommon, the hit the link to enable you to select the SP with which you want SSO.
Issue raised in Github: [oxTrust-2029](https://github.com/GluuFederation/oxTrust/issues/2029)